safe-arithmetic 0.0.3

Traits for safe arithmetic operations in rust
Documentation 
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use crate::error::{Overflow, Underflow};
use std::fmt::{self, Debug, Display};

pub trait CheckedAdd<Rhs = Self>
where
    Self: Sized,
{
    type Output;
    type Error;

    /// Checked arithmetic addition to self
    ///
    /// # Errors
    /// When the result of the addition can not be represented (e.g. due to an overflow).
    fn checked_add(self, rhs: Rhs) -> Result<Self::Output, Self::Error>;
}

macro_rules! impl_unsigned_checked_add {
    ( $T:ty ) => {
        impl CheckedAdd for $T {
            type Output = Self;
            type Error = AddError<Self, Self>;

            fn checked_add(self, rhs: Self) -> Result<Self::Output, Self::Error> {
                num::CheckedAdd::checked_add(&self, &rhs)
                    .ok_or(rhs.overflows(self))
                    .map_err(AddError)
            }
        }
    };
}

impl_unsigned_checked_add!(u32);

macro_rules! impl_signed_checked_add {
    ( $T:ty ) => {
        impl CheckedAdd for $T {
            type Output = Self;
            type Error = AddError<Self, Self>;

            fn checked_add(self, rhs: Self) -> Result<Self::Output, Self::Error> {
                if rhs.is_negative() {
                    num::CheckedSub::checked_sub(&self, &rhs.abs())
                        .ok_or(rhs.underflows(self))
                        .map_err(AddError)
                } else {
                    num::CheckedAdd::checked_add(&self, &rhs)
                        .ok_or(rhs.overflows(self))
                        .map_err(AddError)
                }
            }
        }
    };
}

impl_signed_checked_add!(i64);

#[derive(PartialEq, Clone, Debug)]
#[allow(clippy::module_name_repetitions)]
pub struct AddError<Lhs, Rhs>(pub crate::error::Operation<Lhs, Rhs>);

impl<Lhs, Rhs> crate::error::Arithmetic for AddError<Lhs, Rhs>
where
    Lhs: crate::Type,
    Rhs: crate::Type,
{
}

impl<Lhs, Rhs> std::error::Error for AddError<Lhs, Rhs>
where
    Lhs: Display + Debug,
    Rhs: Display + Debug,
{
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        self.0.cause.as_deref().map(crate::error::AsErr::as_err)
    }
}

impl<Lhs, Rhs> Display for AddError<Lhs, Rhs>
where
    Lhs: Display,
    Rhs: Display,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self.0.kind {
            Some(kind) => write!(
                f,
                "adding {} to {} would {} {}",
                self.0.rhs,
                self.0.lhs,
                kind,
                std::any::type_name::<Lhs>(),
            ),
            None => write!(f, "cannot add {} to {}", self.0.rhs, self.0.lhs,),
        }
    }
}